PE Conversion

[Giovanni Mascellani]

Hi,

Il 19/08/21 17:08, Erich E. Hoover ha scritto:
> 1) 32-bit system libraries are being deprecated by the distros (and
> Apple has already discontinued 32-bit support), so converting built-in
> libraries to PE means that Wine will interface solely with the 64-bit
> system libraries.

My understanding is that this is not just 32 on 64, but can be useful in 
general to run any architecture inside any other, with the help of an 
emulator. Given that ARM already has virtually all mobile devices and it 
is cutting itself a corner even among laptops and desktops, that could 
eventually become something we want to do. Arguably, it is already.

As I get it, the main idea here is that PE libraries are meant to be ran 
in the guest architecture and  ELF libraries are meant to be ran in the 
host architecture. Of course the two must speak to each other, and this 
happens through a well defined interface, where it is (relatively) easy 
to do what the two architectures require to understand each other (enter 
or leave the emulator, change processor mode, convert pointers, 
endianness, sizes, whatever). In particular, PE modules do not need and 
cannot interface directly with the operating system's libraries.

For PE libraries that do not need to interface with host libraries, 
there is little to be done. For PE libraries that have to talk with the 
host system, they need a corresponding ELF library (which is just a 
regular host ELF library, so can link against other host libraries at 
its will). When the PE module is loaded, it calls __wine_init_unix_lib, 
which is intercepted by ntdll, which loads the corresponding ELF library 
and calls its __wine_init_unix_lib function, which returns a point to a 
structure with all the function pointers that the PE library might want 
to call. Given that ntdll mediates this exchange, it will be able to do 
whatever thunking is required to make the interface between the two 
worlds work.

I've heard of a syscall-like mechanism, but I am not sure it is relevant 
here.

This is what I could understand of this business. I'm happy to take 
corrections for whatever I mistook.

Giovanni.